1. Field of the Invention
The invention relates to a fan operation control method and apparatus to control an operating time of an electric fan that cools an internal combustion engine after the internal combustion engine is stopped and an idle speed increase time required for charging the battery.
2. Description of the Related Art
Typically, an internal combustion engine mounted on a vehicle, for example, is relatively hot immediately after the internal combustion engine is stopped. If the internal combustion engine is restarted under such circumstances, fuel in a fuel pipe of a fuel injection system becomes hot (for example, approximately 100° C.), and therefore, bubbles (fuel vapor) are formed and thus the amount of fuel injected is reduced. This makes an air-fuel ratio in each cylinder significantly leaner than a desired air fuel ratio, which can result in unstable engine speed during idling operation (hereinafter referred to as “idle speed”) and can significantly reduce startability of the internal combustion engine. For this reason, it has been proposed to cool an internal combustion engine by operating a fan for a predetermined time after the internal combustion engine is stopped.
As a method to cool the internal combustion engine as described above, a method of controlling a fan motor has been proposed in which an operating time of the fan is calculated using the amount of energy supplied to the internal combustion engine and characteristic values of the fan (for example, refer to Published Japanese Translation of PCT Application No. 2006525462 (JP-A-2006-525462)).
In the control method as proposed above, the operating time of the fan required after the internal combustion engine is stopped is calculated based on an integral value of the measured amount of energy supplied to the internal combustion engine before the internal combustion engine is stopped, and on operational data and ambient environmental data of the internal combustion engine at the present time. After the internal combustion engine is stopped, the fan is operated using electric power supplied from the battery. Then, the electric power of the battery consumed after the internal combustion engine is stopped is compensated by charging the battery using electric power generated by an electric generator that is driven to rotate by the internal combustion engine after the internal combustion engine is restarted.
On the other hand, even during normal operation of the internal combustion engine, if an electrical component that consumes a large amount of electricity is used during idling, the capacity of the electric generator becomes insufficient to cover the electric load required to supply electricity to the electrical component at the normally set idle speed. Therefore, a technology has been proposed in which the set idle speed is corrected to increase as the electric load increases (for example, refer to Japanese Patent Application Publication No. 61-70149 (JP-A-61-70149)).
According to the technology described above, detection means for detecting charge/discharge condition of the battery is provided, and when the detection means detects that the battery is discharging due to increase of the electric load, control means corrects the idle speed to increase.
However, according to the technology described in JP-A-2006-525462, the operating time of the fan is calculated based on the amount of energy supplied to the internal combustion engine and the characteristic values of the fan. It is difficult to accurately measure these values, and as a result, it is also difficult to calculate the fan operating time. Further, according to the technology described in JP-A-2006-525462, because the operating time of the fan after the internal combustion engine is stopped fluctuates, it is not possible to effectively charge the battery to compensate for the decrease in the battery charge amount. For example, if a battery charging time is set in order to sufficiently charge the battery at all times, the battery is unnecessarily charged when the operating time of the fan is short.
Further, according to the technology described in JP-A-61-70149, it is detected whether the battery is discharging due to increase in the electric load. If it is detected that the battery is discharging, the idle speed is corrected to increase. Therefore, a plurality of devices, such as a comparator and a delay circuit, are required, and further, a complicated circuit is also required. Further, according to the technology described in JP-A61-70149, the idle speed can be increased only when the battery is discharging, and it is not possible to deal with the decrease in the battery charge amount after the internal combustion engine is stopped.